We report on the evidence for a strong low-energy spectral
cutoff in the radio-loud quasar RXJ1028.6-0844 at a redshift
of 4.28 obtained with an ASCA observation. The most likely
explanation is photoelectric absorption of the soft X-rays.
Our result confirmed that the excess X-ray absorption is
common for radio-loud quasars at redshifts extending up to
z>4. If the absorber lies close to the quasar, the derived
H column density (~2\times 1023\,cm-2) is the
largest among those found in high-redshift radio quasars.
This may indicate the presence of a remarkably large amount
of obscuring matter in the quasar environment in the early
universe. Possible origins of the absorber are discussed.